Method and apparatus for electromagnetic irradiation of liquid

ABSTRACT

An electromagnetic wave applying apparatus having an electromagnetic wave source ( 13 ) such as an ultraviolet lamp or the like, a cylinder ( 15 ) surrounding the electromagnetic wave source, a liquid retention tank ( 16 ) disposed around the cylinder, and an inlet portion ( 17 ) for introducing a liquid overflow from the liquid retention tank as a thin film flowing down an inner wall surface of the cylinder, which is irradiated with an electromagnetic wave from the ultraviolet lamp ( 11 ). The electromagnetic wave applying apparatus also has swirling flow forming means for causing the liquid introduced from the inlet portion ( 17 ) onto the inner wall surface of the cylinder to flow as a swirling flow down the inner wall surface. The electromagnetic wave applying apparatus allows a large amount of liquid to be stably treated by the application of an electromagnetic wave without causing the electromagnetic wave source such as an ultraviolet lamp or the like to be contaminated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for and a method ofapplying an electromagnetic wave to a liquid, and more particularly toan apparatus for and a method of applying an electromagnetic wave suchas ultraviolet rays or the like to various liquids including water beingprocessed in wastewater treatment plants, industrial drains, water forvarious uses, sewage, purified water, drinking water, pure water,ultrapure water, etc.

2. Description of Related Art

The application of electromagnetic waves such as ultraviolet rays or thelike to liquids is widely used for the purposes of treating orsterilizing trace amounts of contaminants by way of excitation and/ordissociation of molecular bonds of organic substances or oxidizingagents. According to such a process, ultraviolet rays and an oxidizingagent such as ozone are used together to generate OH radicals, whichdecompose underwater contaminants by way of oxidization. The processdoes not produce secondary waste materials and is capable of decomposingdioxins and so on in water.

It is customary to apply ultraviolet rays to a liquid to be treated froman ultraviolet lamp which is sealed in a watertight fashion by atransparent protective tube of quartz and immersed in a tank thatcontains the liquid to be treated. When the protective tube sealing theultraviolet lamp is immersed in the liquid to be treated, inorganicsubstances such as metals (iron, manganese, etc.) in the liquid ororganic substances in the liquid are attached to the outercircumferential surface of the transparent protective tube, depositing acovering thereon which tends to lower the radiated intensity of theultraviolet rays.

There is known another method of treating a liquid by letting the liquidflow in the form of a thin film down a vertical wall surface andirradiating the liquid with an electromagnetic wave such as ultravioletrays or the like emitted from a position spaced from the liquid. Sincethe source of the electromagnetic wave such as ultraviolet rays or thelike is positioned remotely from the liquid, the method is effective toprevent the problem that contaminants are attached to a protective tubeor the like of an electromagnetic wave source, lowering the radiatedintensity. However, the distance between the electromagnetic wave sourceand the liquid to be treated poses a problem. Specifically, if thedistance between the electromagnetic wave source and the liquid to betreated is large, then the radiated intensity of the electromagneticwave is reduced. If the distance between the electromagnetic wave sourceand the liquid to be treated is reduced and the electromagnetic wavesource and the liquid to be treated are positioned closely to eachother, then the radiated intensity of the electromagnetic wave can beachieved, but it is difficult to form a stable, high-speed thin film ofliquid flowing down a vertical wall surface. In case the amount of theliquid to be treated is small, a thin film of liquid can be formed whichcan sufficiently be irradiated with an electromagnetic wave. In case theamount of the liquid to be treated is large, however, the thickness ofthe film of liquid flowing down is increased, and when the speed of theflowing liquid is increased, the thin film of liquid becomes unstable,producing splashes which are scattered and contaminate theelectromagnetic wave source.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above drawbacks. Itis an object of the present invention to provide an apparatus for and amethod of applying an electromagnetic wave to treat a large amount ofliquid stably without causing an electromagnetic wave source to becontaminated.

According to the present invention, an electromagnetic wave applyingapparatus comprises an electromagnetic wave source, a cylindersurrounding the electromagnetic wave source, a liquid retention tankdisposed around the cylinder, and an inlet portion for introducing aliquid overflow from the liquid retention tank as a thin film flowingdown an inner wall surface of the cylinder, which is irradiated with anelectromagnetic wave from the electromagnetic wave source, wherein theinlet portion has a curved surface joining an overflow portion of theliquid retention tank to the inner wall surface of the cylinder.

Since the overflow portion of the liquid retention tank and the innerwall surface of the cylinder are connected to each other by the curvedsurface of the inlet portion, a thin-film liquid layer can be formedstably on the inner wall surface of the cylinder even if the liquidflows in a large quantity. Consequently, the electromagnetic waveapplying apparatus can increase the amount of the liquid treated therebywithout contaminating the electromagnetic wave source.

The electromagnetic wave applying apparatus preferably includes swirlingflow forming means for causing the liquid introduced from the inletportion onto the inner wall surface of the cylinder to flow as aswirling flow down the inner wall surface.

According to another aspect of the present invention, an electromagneticwave applying apparatus comprises an electromagnetic wave source, acylinder surrounding the electromagnetic wave source, a liquid retentiontank disposed around the cylinder, an inlet portion for introducing aliquid overflow from the liquid retention tank as a thin film flowingdown an inner wall surface of the cylinder, which is irradiated with anelectromagnetic wave from the electromagnetic wave source, and swirlingflow forming means for causing the liquid introduced from the inletportion onto the inner wall surface of the cylinder to flow as aswirling flow down the inner wall surface.

Even when the liquid splashes, since the direction of the liquidsplashes is tangential to the inner wall surface of the cylinder, theprotective tube disposed at the center of the cylinder is prevented frombeing contaminated by liquid splashes. The liquid flowing down the innerwall surface of the cylinder is subject to centrifugal forces, producingthe thin film of the liquid uniformly and stably.

The inner wall surface of the cylinder is preferably slanted such thatthe diameter thereof is greater upwardly and smaller downwardly. Withthe slanted inner wall surface, the liquid is not peeled off the innerwall surface of the cylinder, and flows smoothly down the inner wallsurface.

Preferably, the electromagnetic wave comprises ultraviolet rays and theelectromagnetic wave source comprises an ultraviolet lamp.

According to the present invention, a method of applying anelectromagnetic wave to a liquid comprises; introducing a liquid along acurved surface to an inner wall surface of a cylinder from an upper endthereof, flowing the liquid to flow as a thin film down the inner wallsurface of the cylinder; and applying an electromagnetic wave from anelectromagnetic wave source disposed substantially centrally in thecylinder to the liquid.

The electromagnetic wave is preferably applied to the liquid while theliquid is flowing as a swirling thin film down the inner wall surface ofthe cylinder from the upper end thereof.

According to another aspect of the present invention, a method ofapplying an electromagnetic wave to a liquid comprises; flowing a liquidto flow as a swirling thin film down an inner wall surface of a cylinderfrom the upper end thereof; and applying an electromagnetic wave to theliquid from an electromagnetic wave source disposed substantiallycentrally in the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of an apparatus for applyingultraviolet rays to a liquid according to an embodiment of the presentinvention;

FIG. 2 is a plan view of the ultraviolet applying apparatus shown inFIG. 1;

FIGS. 3A through 3C are views showing various shapes of an inlet portionon an upper portion of the inner wall surface of a cylinder;

FIG. 4 is a view of a modification of the ultraviolet applying apparatusshown in FIG. 1, showing the slanted inner wall surface of a cylinder;

FIG. 5 is a vertical cross-sectional view of an ultraviolet applyingapparatus according to a comparative example in which an ultravioletsource is immersed in a liquid;

FIG. 6 is a plan view showing a uniform thin film of liquid formed onthe inner wall surface of a cylinder;

FIG. 7 is a plan view showing a liquid retention tank according to acomparative example in which an inflow tube is attached perpendicularlyto a side wall of the liquid retention tank;

FIG. 8 is a vertical cross-sectional view showing a liquid retentiontank according to a comparative example in which inflow tubes areattached perpendicularly to a bottom wall of the liquid retention tank;

FIG. 9 is a plan view showing an irregular thin film of liquid formed onthe inner wall surface of a cylinder; and

FIG. 10 is a vertical cross-sectional view of an ultraviolet applyingapparatus according to a comparative example which has a right-angularinlet portion.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a cross-sectional structure of an electromagnetic waveapplying apparatus according to an embodiment of the present invention,and FIG. 2 shows a plan structure of the electromagnetic wave applyingapparatus. The electromagnetic wave applying apparatus according to theembodiment of the present invention has an ultraviolet lamp 11 disposedcentrally therein for applying ultraviolet rays which are a type ofelectromagnetic wave and a protective tube 12 of transparent quartzglass or the like surrounding the ultraviolet lamp 11 for protecting theultraviolet lamp 11 against direct contact with splashes. Theultraviolet lamp 11 and the protective tube 12 jointly make up anelectromagnetic wave source 13, around which a cylinder 15 is coaxiallydisposed. The electromagnetic wave source 13 applies ultraviolet rays toa thin-film liquid layer W flowing down the inner wall surface of thecylinder 15. A liquid retention tank 16 is disposed around the cylinder15 and stores a liquid which overflows the upper end of the liquidretention tank 16 and flows down the inner wall surface of the cylinder15. If a plurality of cylinders is employed, then they may share theliquid retention tank disposed therearound.

The upper end of the liquid retention tank 16 has an inlet portion 17for introducing the liquid overflow as a thin film flowing down theinner wall surface of the cylinder 15 which is irradiated by theelectromagnetic wave source 13. The inlet portion 17 is defined by abell-mouthed surface which is curved so as to be smoothly joined to theinner wall surface of the cylinder 15. The electromagnetic wave applyingapparatus also has a swirling flow forming means for causing the liquidto flow as a swirling flow down the inner wall surface of the cylinder15. Specifically, the liquid retention tank 16 has an inflow tube 18fixedly connected to the bottom thereof for introducing the liquid intothe liquid retention tank 16 tangentially to the outer circumferentialsurface of the liquid retention tank 16, as shown in FIG. 2. Therefore,the introduced liquid is delivered upwardly while swirling around alongthe inner surface of the outer circumferential wall of the liquidretention tank 16, flows down the curved surface of the inlet portion 17from the upper overflow end of the liquid retention tank 16, and thenflows as a swirling flow down the inner wall surface of the cylinder 15.On the inner wall surface of the cylinder 15 which is irradiated by theelectromagnetic wave source 13, therefore, the liquid W is irradiatedwith ultraviolet rays while swirling around and flowing down as a thinfilm. In the example shown in FIG. 2, the inflow tube is connectedtangentially to the outer circumferential surface of the liquidretention tank 16. However, the inflow tube may be connected at anyangle capable of forming a swirling flow in the liquid retention tank16, rather than tangentially to the outer circumferential surface of theliquid retention tank 16.

FIGS. 3A through 3C show the various shapes of the inlet portion. Thebell-mouthed surface signifies an opening surface of a bell (a curvedinner circumferential surface). The smoothly curved surface joins theinlet portion from the overflow end of the liquid retention tank 16 tothe inner wall surface of the cylinder 15 which is substantiallyvertical. FIG. 3A shows a curved surface defined by an arc which isone-quarter of a true circle having a diameter of d. FIG. 3B shows acurved surface defined by an arc which is one-quarter of an oblongcircle. FIG. 3C shows a smooth profile defined by a combination of anarc having a radius of R₁ and an arc having a radius of R₂. In each ofthese configurations, the ratio (d/D) of the radius d of thebell-mouthed arc to the diameter D of the inner wall surface of thecylinder 15 should preferably be 0.1 or higher. The arc shouldpreferably be an arc in the range from 3/16 to 8/16.

The electromagnetic wave applying apparatus operates as follows:Ultraviolet rays which is a type of electromagnetic wave are appliedfrom the ultraviolet lamp 11 disposed in the protective tube 12 to athin film of the liquid W flowing down the inner wall surface of thecylinder 15. When the liquid layer flows over the upper overflow end ofthe inner wall surface of the cylinder 15 and down as a thin film alongthe inner wall surface of the cylinder 15, it is introduced through theinlet portion 17 in the form of a curved surface onto the inner wallsurface of the cylinder 15. Therefore, the overflow from the liquidretention tank 16 is smoothly introduced as a thin film onto the innerwall surface of the cylinder 15, and smoothly flows down the inner wallsurface of the cylinder 15. Therefore, there is produced a downwardlyflowing liquid layer of uniform thickness without producing splashes andthickness irregularities. As the liquid swirls in the liquid retentiontank 16 and forms a downwardly flowing layer from the inlet portionalong the inner wall surface of the cylinder 15, the liquid is subjectto centrifugal forces and has its surface stabilized and/or uniformized,so that the liquid overflow is supplied from all locations on the inletportion at a constant rate to the inner wall surface of the cylinder 15which is irradiated with ultraviolet rays. Since the liquid is given aswirling flow speed, even if the liquid contains suspended materials,they are prevented from being settled and/or accumulated in the liquidretention tank 16. Even when the liquid splashes, the liquid isscattered tangentially to the inner wall surface of the cylinder, ratherthan centrally toward the protective tube 12. Consequently, the liquidsplashes are prevented from being applied to the protective tube 12,which is thus prevented from being contaminated. Furthermore, thethickness of the liquid layer is uniformized as the liquid is subject tocentrifugal forces because of the swirling flow thereof. Due to thecentrifugal forces acting on the liquid, the thin-film liquid on theinner wall surface of the cylinder 15 is retained thereon for a periodof time longer than if there were no swirling flow thereon.

As shown in FIG. 4, the inner wall surface of a cylinder 15A which isirradiated with ultraviolet rays may be progressively smaller indiameter from the upper portion to the lower portion thereof. Accordingto this modification, the liquid layer produced by the liquid that flowsin from the inlet portion is prevented from being peeled off the innerwall surface of the cylinder 15A which is irradiated with ultravioletrays. Therefore, even when the liquid is supplied in a large quantity, athin-film liquid layer can stably be formed on the inner wall surface ofthe cylinder 15A.

Preferred structural examples of various parts of the electromagneticwave applying apparatus will be described below. The light source forsupplying ultraviolet rays as an electromagnetic wave should preferablybe a light source capable of emitting ultraviolet rays havingwavelengths ranging from 170 to 380 nm, such as a low-pressure mercurylamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, anexcimer laser, a black light, or the like. Other electromagnetic wavesources than the ultraviolet lamp, such as those for emitting anyvisible light, infrared rays, X-rays, gamma rays, radio waves, or thelike, may be employed. The protective tube used to prevent theultraviolet lamp from being damaged and smeared should preferably bemade of natural quartz glass or synthetic quartz glass. The protectivetube may be of a double-walled tube structure having two quarts tubes ofdifferent diameters, with a liquid or a gas flowing therebetween forcooling the UV lamp.

The electromagnetic wave source 13 should preferably be installedvertically at the center of the inner wall surface of the cylinder 15which is irradiated with ultraviolet rays. As described above, the innerwall surface of the cylinder may be slightly slanted. Theelectromagnetic wave source 13 thus arranged is capable of supplying auniform amount of ultraviolet rays dose in all directions around.

Raw liquids to be irradiated with ultraviolet rays may be polluted waterincluding leachate from final disposal sites, industrial drains, waterfor various uses, sewage, etc., liquids including potable water,purified water, drinking water, pure water, ultrapure water, etc.,liquids containing organic substances or organisms such as bacteria, andliquids containing, together with organic substances, oxidizing agentsincluding ozone, hydrogen peroxide, and sodium hypochlorite,heterogeneous catalysts such as titanium dioxide, and homogeneouscatalysts such as iron ions. Substances in the liquid to be treated maybe hardly biodegradable organic substances such as fumin acid, endocrinedisruptors including dioxin, bisphenol-A, nonylphenol,diethylhexyldioxane phathalate, etc., organic chlorine compoundsincluding carcinogen, trichloroethylene, chlorophenol, pesticides, TOX(Total Organic Halogen), etc. Furthermore, escherichia coli, generalbacteria, and protozoa such as cryptospordium may also be substances inthe liquid to be treated.

The inner wall of the cylinder 15 which is irradiated withelectromagnetic waves may be made of synthetic resins such as vinylchloride, metals such as stainless steel, glass, and ceramics. If theliquid is mainly composed of water, then the surface of the inner wallmay be combined with a hydrophilic material such as titanium dioxide,for example, for forming a thin film of liquid more stably. Ifultraviolet rays are applied to titanium dioxide, then active oxygen isgenerated from dissolved oxygen, making organic substances moredegradable. The inner wall surface of the cylinder 15 which isirradiated with electromagnetic waves may be of an ordinary cylindricalshape for producing a thin-film liquid layer. For stably forming athin-film liquid layer from a large amount of liquid, however, the innerwall surface of the cylinder should preferably have a bell-mouthed upperportion and be progressively larger in diameter upwardly in a curvedconfiguration.

Treating conditions in the electromagnetic wave applying apparatusaccording to the present invention may be selected depending on theamount of the liquid, the diameter and length of the electromagneticwave source such as an ultraviolet lamp, the diameter of the protectivetube, the diameter of the inner wall, and the ultraviolet rays dose. Forexample, treating conditions for the use of ultraviolet rays, anultraviolet lamp having a length of 1200 mm or less, and a protectivetube having a diameter in the range from 30 to 40 mm will be describedbelow.

The diameter of the cylinder which is irradiated with ultraviolet raysis selected normally in a range from 50 to 300 mm, or preferably in arange from 100 to 260 mm. The length of the portion of the cylinderwhich is irradiated with ultraviolet rays is longer than the ultravioletlamp, and is selected normally in a range from 1 to 4 times the emissionlength of the ultraviolet lamp, or preferably in a range from 1.5 to 3times the emission length of the ultraviolet lamp. The differencebetween the diameter of the inner circumferential surface of the outerwall of the liquid retention tank and the diameter of the outercircumferential surface of the inner wall of the liquid retention tankis selected normally in a range from 5 to 130 mm, or preferably in arange from 30 to 80 mm. If a low-pressure mercury lamp or amedium-pressure mercury lamp is used, then the ultraviolet dose isselected normally in a range from 0.005 to 5.0 w·hr/l, or preferably ina range from 0.01 to 3.0 w·hr/l. If a large ultraviolet dose isrequired, then the liquid may be repeatedly passed through the cylinder.The thickness of the thin-film liquid layer flowing down the inner wallsurface of the cylinder is normally in a range from 1 to 5 mm, orpreferably in a range from 2 to 4 mm. The overflow load imposed when theliquid flows from the liquid retention tank 16 onto the inner wallsurface which is irradiated with ultraviolet rays is normally in a rangefrom 100 to 600 m³/m·day, or preferably in a range from 200 to 500m³/m·day. The speed of the swirling flow in the liquid retention tank 16is normally in a range from 20 to 100 cm/second, or preferably in arange from 30 to 80 cm/second.

Specific examples of the present invention will be described below.However, the present invention is not limited to those specificexamples.

EXAMPLE 1

Using the apparatus shown in FIGS. 1 and 2, a liquid having a COD(Chemical Oxygen Demand) of 50 mg/l, TOX of 1 mg/l, an ironconcentration of 5 mg/l, a manganese concentration of 5 mg/l, and adissolved O₂ concentration of 10 mg/l was treated with ultraviolet raysunder the following conditions:

Ultraviolet lamp: medium-pressure mercury lamp (2 kW, the emissionlength of 350 mm)

Protective tube: outside diameter of 33 mm, made of ordinary quartzglass

Diameter of the inner wall surface of the cylinder: 200 mm

Bell-mouthed surface: defined by an arc which is one-quarter of a truecircle having a diameter of d=30 mm

Flow rate of the liquid: 200 l/minute

Speed of the swirling flow: 80 cm/second

Operating time: 24 hours

As a result, the applied intensity of the ultraviolet rays after elapseof 24 hours was 98% of the initial level, and hence the appliedintensity of the ultraviolet rays was substantially constant throughoutthe operating time of 24 hours. This indicates that the outercircumferential surface of the protective tube was not smeared bysplashes of the liquid, etc. The COD and TOX of the treated water were45 mg/l and 0.1 mg/l, respectively, on the average after elapse of 24hours, and were reduced by 5 mg/l and 0.9 mg/l, respectively. Theseresults show that a good effect was achieved by the application of theultraviolet rays.

In a comparative example, the same liquid was irradiated withultraviolet rays using an apparatus shown in FIG. 5 under the conditionsshown below. In the apparatus shown in FIG. 5, an electromagnetic wavesource (ultraviolet source) 13 comprising an ultraviolet lamp 11 sealedin a watertight fashion by a protective tube 12 of quartz glass wasimmersed in a liquid to be treated within a cylindrical container 20.

Ultraviolet lamp: medium-pressure mercury lamp (2 kW, the emissionlength of 350 mm)

Protective tube: outside diameter of 33 mm, made of ordinary quartzglass

Diameter of the portion irradiated with ultraviolet rays: 200 mm

Flow rate of the liquid: 200 l/minute

Operating time: 24 hours

As a result, the applied intensity of the ultraviolet rays after elapseof 24 hours was 10% of the initial level, and hence the appliedintensity of the ultraviolet rays had a tendency to drop greatly withtime. This indicates that the surface of the protective tube was smearedby metal components or organic substances in the treated liquid,lowering the applied intensity of the ultraviolet rays. As a result, thereductions in the COD, TOX, etc. were lowered. The COD and TOX of thetreated water were 49 mg/l and 0.8 mg/l, respectively, on the averageafter elapse of 24 hours, and were reduced by 1 mg/l and 0.2 mg/l,respectively, which were much smaller than those in above Example 1.These results show that the apparatus according to the present inventionis capable of decomposing COD and TOX components while substantiallyfully preventing the protective tube from being contaminated.

EXAMPLE 2

Using the apparatus shown in FIGS. 1 and 2, a liquid having ahexachlorobenzene concentration of 10 μg/l, an iron concentration of 5mg/l, and a manganese concentration of 5 mg/l was treated withultraviolet rays under the same conditions as those of Example 1:

As a result, the applied intensity of the ultraviolet rays after elapseof 24 hours remained substantially unchanged, and hence wassubstantially constant throughout the 24 hours. The hexachlorobenzeneconcentration in the treated water was 8 μg/l on the average, and wasreduced by 2 μg/l. Almost all decomposed products were chlorobenzenehaving a chlorine number of 5 or less. These results show that adechlorinating reaction is possible according to the present invention.

EXAMPLE 3

Using the apparatus shown in FIGS. 1 and 2, a liquid having a COD(Chemical Oxygen Demand) of 50 mg/l, TOX of 1 mg/l, an ironconcentration of 5 mg/l, a manganese concentration of 5 mg/l, and adissolved O₂ concentration of 10 mg/l was treated with ultraviolet raysunder the following conditions:

Ultraviolet lamp: medium-pressure mercury lamp (2 kW, the emissionlength of 350 mm)

Protective tube: outside diameter of 33 mm, made of ordinary quartzglass

Diameter of the inner wall surface irradiated with ultraviolet rays: 200mm

Bell-mouthed surface: defined by an arc which is one-quarter of a truecircle having a diameter of d=30 mm

Flow rate of the liquid: 50 to 250 l/minute

Operating time: 24 hours

Speed of the swirling flow in the liquid retention tank: 20 to 100cm/second

As a result, the thin-film liquid layer on the inner wall surface of thecylinder was formed stably under the conditions of the flow rates up to250 l/minute, and essentially no splashes were recognized. The thicknessof the thin-film liquid layer W was uniform in any location thereon asshown in FIG. 6. The ratio of the ultraviolet rays that have passedthrough the protective tube after 24 hours was 98% or more of theinitial level under any of the above conditions, and almost no reductionin the intensity of the ultraviolet rays was recognized.

In Comparative Example 1, an inflow tube 18 was attached perpendicularlyto the outer circumferential surface of a liquid retention tank 16, asshown in FIG. 7. FIG. 8 shows inflow tubes 18 attached perpendicularlyto a bottom wall of a liquid retention tank 16. In these ultravioletapplying apparatus, no swirling flow is developed in the liquidretention tank, and there is no swirling flow speed created on the innerwall surface of the cylinder 15. As a result, when these ultravioletapplying apparatus were used, the thin-film liquid layer W on the innerwall surface of the cylinder suffered thickness irregularities shown inFIG. 9 at liquid flow rates starting from 100 l/minute. The liquidproduced splashes much more than if a swirling flow was formed. Theratio of the ultraviolet rays that have passed through the protectivetube after 24 hours dropped to 50% of the initial level at liquid flowrates of 150 l/minute and higher.

A comparison based on whether a swirling flow is produced or notindicates that the stability of the thin-film liquid layer W, theuniformity of the thickness thereof, and the flow rate load were betterwhen a swirling flow was produced.

According to Comparative Example 2, a right-angular inlet portion 17 wasemployed as shown in FIG. 10 and there is no swirling flow developed.Other conditions were the same as those of Example 3.

At a flow rate of 100 l/minute, the thin film was irregular, and theliquid produced fine splashes, which were attached frequently to theprotective tube 12. The ratio of the ultraviolet rays that have passedthrough the protective tube after 24 hours dropped to 40% of the initiallevel at a liquid flow rate of 100 l/minute.

When the liquid flow rate exceeded 100 l/minute, the thin film waspeeled off the inner wall surface of the cylinder and ruptured, and wasapplied to the surface of the protective tube 12 disposed centrally inthe cylinder, as indicated by the dotted lines W′ in FIG. 10.

In each of the above embodiments, trace amounts of substances in thewater were treated by the application of ultraviolet rays. However,lamps of other wavelengths may be used as the electromagnetic wavesource for other applications. Thus, electromagnetic waves of variouswavelengths may be used as the electromagnetic wave source.

The cylinder described above refers to an object capable of forming athin-film liquid layer when the liquid flows down smoothly therealong.Therefore, the concept of the cylinder according to the presentinvention includes a polygonal prism, an oblate cylinder, or a similarshape which is effective to provide the above effect.

According to the present invention, as described above, a large amountof liquid can be treated by being stably irradiated with anelectromagnetic wave. Specifically, the electromagnetic wave is appliedfrom the electromagnetic wave source disposed in the protective tube tothe liquid flowing as a thin film down the inner wall surface which isirradiated with the electromagnetic wave. (1) Because the inlet portionfor introducing the liquid overflow from the liquid retention tank ontothe inner wall surface of the cylinder has a curved surface, the stateof the surface of the liquid is stabilized and/or uniformized, and theliquid overflow is supplied from all locations on the inlet portionsmoothly at a constant speed. (2) Since a swirling flow speed is givento the liquid, even if the liquid contains suspended materials, they areprevented from being settled and/or accumulated in the liquid retentiontank. Even when the liquid splashes while the liquid overflow flows downas a thin film from the upper end of the surface irradiated withultraviolet rays, because the liquid is scattered tangentially to theinner wall surface of the cylinder, rather than centrally toward theprotective tube, the protective tube is prevented from beingcontaminated by the liquid splashes. The thin film of the liquid on theinner wall surface which is irradiated with ultraviolet rays is subjectto centrifugal forces because the liquid is swirling, so that the thinfilm is uniformly and stably formed, and its thickness is uniformized.(3) If the cylinder which is irradiated with ultraviolet rays has aslanted portion which is progressively larger in diameter upwardly, thenthe liquid is prevented from being peeled off the surface irradiatedwith ultraviolet rays while the liquid overflows is flowing down as athin film therealong. Therefore, even when the liquid flows down in alarge amount, the thin film of the liquid is stably formed.

INDUSTRIAL APPLICABILITY

The present invention is concerned with an apparatus for and a method ofapplying an electromagnetic wave such as ultraviolet rays or the like tovarious liquids including water being processed in wastewater treatmentplants, industrial drains, water for various uses, sewage, purifiedwater, drinking water, pure water, ultrapure water, etc. The inventionis appropriately applicable to water treatments in various fields fordecomposing trace amounts of contaminants by applying an electromagneticwave such as ultraviolet rays or the like to various liquids in theabove fields.

What is claimed is:
 1. An electromagnetic wave applying apparatuscomprising: a cylinder having an inner wall surface; an inlet portiondisposed at a top end of said cylinder and having a curved surface, saidinlet portion being connected to the top end of said cylinder so thatthe curved surface smoothly joins with the inner wall surface of saidcylinder; a liquid retention tank disposed around said cylinder forstoring a liquid and introducing the liquid over said inlet portion,said liquid retention tank including a swirling flow forming portion;and an electromagnetic wave source centrally disposed in said cylinder,wherein said cylinder is coaxially disposed around said electromagneticwave source to permit a thin film liquid layer to flow over said inletportion and down along the inner wall surface of said cylinder so thatthe thin film liquid layer can be irradiated with an electromagneticwave emitted from said electromagnetic wave source, and wherein saidswirling flow forming portion is operable to cause the liquid introducedfrom said inlet portion into said cylinder to flow as a swirling flowdown the inner wall surface.
 2. An electromagnetic wave applyingapparatus according to claim 1, wherein said swirling flow formingportion forms a swirling flow in said liquid retention tank and liquidoverflow from said liquid retention tank is introduced to said inletportion at an upper end thereof.
 3. An electromagnetic wave applyingapparatus comprising: a cylinder having an inner wall surface; an inletportion disposed at a top end of said cylinder and having a curvedsurface, said inlet portion being connected to the top end of saidcylinder so that the curved surface smoothly joins with the inner wallsurface of said cylinder; a liquid retention tank disposed around saidcylinder for storing a liquid and introducing the liquid over said inletportion, said retention tank comprising an inflow tube tangentiallyconnected to a bottom portion of said liquid retention tank at an outercircumferential surface thereof so as to cause a swirling flow in saidliquid retention tank; and an electromagnetic wave source centrallydisposed in said cylinder, wherein said cylinder is coaxially disposedaround said electromagnetic wave source to permit a thin film liquidlayer to flow over said inlet portion and down along the inner wallsurface of said cylinder so that the thin film liquid layer can beirradiated with an electromagnetic wave emitted from saidelectromagnetic wave source.
 4. An electromagnetic wave applyingapparatus according to claim 1, wherein said curved surface comprises anarc, which is one-quarter of a true circle.
 5. An electromagnetic waveapplying apparatus according to claim 1, wherein said curved surfacecomprises an arc, which is one-quarter of an oblong circle.
 6. Anelectromagnetic wave applying apparatus according to claim 1, whereinsaid top portion and said cylinder are arranged so that the thin filmliquid layer will form with uniform thickness without producing splashesand thickness irregularities.
 7. An electromagnetic wave applyingapparatus according to claim 1, wherein said inner wall surface of saidcylinder is substantially vertical.
 8. An electromagnetic wave applyingapparatus according to claim 1, wherein said inner wall surface of saidcylinder is slanted so that an upper diameter thereof is greater than alower diameter thereof.
 9. An electromagnetic wave applying apparatusaccording to claim 1, wherein said electromagnetic wave source isoperable to emit ultraviolet rays.
 10. An electromagnetic wave applyingapparatus according to claim 1, wherein said electromagnetic wave sourcecomprises an ultraviolet lamp and a protective tube.
 11. A method ofapplying an electromagnetic wave to a liquid, the method comprising:introducing a liquid into an upper end of a cylinder so that the liquidflows down along an inner wall surface of the cylinder as a swirlingthin film; and applying an electromagnetic wave to the swirling thinfilm of liquid from an electromagnetic wave source disposedsubstantially centrally in the cylinder.
 12. A method of applying anelectromagnetic wave to a liquid according to claim 11, wherein theliquid is introduced to the cylinder along a curved surface disposed atan upper end of the cylinder.
 13. A method of applying anelectromagnetic wave to a liquid according to claim 11, wherein theinner wall surface of the cylinder is substantially vertical.
 14. Amethod of applying an electromagnetic wave to a liquid according toclaim 11, wherein the inner wall surface of said cylinder is slanted sothat a diameter of the cylinder is greater at an upper portion thereofthan at a lower portion thereof.
 15. A method of applying anelectromagnetic wave to a liquid according to claim 11, wherein thecylinder is coaxially disposed around the electromagnetic wave source.16. A method of applying an electromagnetic wave to a liquid accordingto claim 11, wherein the electromagnetic wave applied to the swirlingthin film of liquid comprises ultraviolet rays.
 17. A method of applyingan electromagnetic wave to a liquid according to claim 11, wherein saidelectromagnetic wave source comprises an ultraviolet lamp and aprotective tube.